The terminals of an electrochemical cell are normally low in electrical resistance, high in corrosion resistance, aesthetically appealing, resistant to mechanical failure and inexpensive. Such varied qualities cannot generally be achieved by the use of a single metal or metal alloy.
Metals possessing good corrosion resistance and aesthetic appeal are expensive and generally possessed of mechanical properties unacceptable in cell terminals. Those inexpensive metals formable into cell terminals of the desired mechanical properties, are generally of poor corrosion resistance and lack aesthetic appeal.
Terminals having the desired properties can be made by coating a thin layer of an expensive, corrosion resistant metal onto a low cost base metal of desired mechanical properties. An example of the use of metal plating in electrochemical cells is found in button cells which are used in watches, hearing aids and the like. The cathode terminals of many such cells are shaped steel members plated with a thin layer of gold or other highly corrosion resistant metal. The gold imparts the desired corrosion resistance and low electrical resistance, and generally improves the aesthetic appearance of the cells.
The recent dramatic increases in the price of gold and of the other metals useful as a cover layer for a cell terminal have caused plated terminals to become increasingly expensive to manufacture. Obvious methods of reducing manufacturing costs are not useful. Costs cannot be reduced simply by decreasing the thickness of the plated metal, since a reduction from the presently used thickness results in a substantial loss of the desired properties imparted by the plated metal. Modern plating processes are otherwise quite efficient and have heretofore not been modifiable to reduce the quantity of metal consumed in plating the terminals.